Many known devices include a firing mechanism activatable by movement of a trigger. The devices are typically for firing or launching a projectile. Typically, the trigger is moved by imposing a trigger pull load on the trigger, to cause the trigger to move from a loaded position, at which the firing mechanism is activatable, to a released position, at which the firing mechanism is activated. Activation of the firing mechanism is conventionally effected in various ways, e.g., via release of an element of the firing mechanism, or otherwise initiating movement of an element of the firing mechanism. As is well known in the art, for various reasons, it is desirable that the trigger pull load be predictable, i.e., consistent for the user. For instance, the device can be more accurately aimed upon firing if the trigger pull load is consistent for the user. Also, in general, a trigger that requires a more consistent trigger pull load is more safely operated.
There are competing factors to be taken into account in determining the trigger pull load required to move the trigger. If the trigger pull load required is relatively large, then an inadvertent activation of the firing mechanism is unlikely. However, it is also desirable that the trigger pull load be relatively small, to make activating the firing mechanism relatively easy. This is generally thought to be desirable because it facilitates maintaining an accurate aim of the device when the trigger is pulled.
Those skilled in the art would be aware of various devices including firing mechanisms activatable by movement of a trigger. One example of a device including a firing mechanism activatable by a trigger is a crossbow, i.e., a high-powered weapon designed to shoot arrows (or bolts) at a target. As is well known in the art, the crossbow may include, for example, a stock with a bow mounted transversely on it. A bowstring across the bow is pulled taut, and the bolt is positioned to be propelled by the bowstring upon the bowstring's release. Typically, the taut bowstring is held in a cocked position by the firing mechanism, which is activatable by moving the trigger in a trigger mechanism to the released position thereof. However, the typical trigger mechanism has a number of deficiencies.
Typical draw forces for a crossbow vary from 100 to 250 lbs. As is well known in the art, it is desirable that such high loads should be dealt with by the trigger mechanism at relatively low trigger efforts (i.e., relatively low trigger pull loads), for shooting accuracy. However, known triggers rely on friction between the ticker (or trigger) and sear surfaces and as a result they have relatively high trigger pull efforts or loads, e.g., in the range of approximately 2.5 lbs. to approximately 9 lbs. (approximately 1.134 kg. to approximately 4.082 kg.).
In the prior art, to lower the coefficient of friction, certain techniques are employed (e.g., ticker and sear surfaces are polished, and/or lubrication is applied) in order to mitigate the relatively high trigger pull efforts. However, at best, the coefficient of friction is not lower than 0.1 in the conventional trigger mechanism. Even with those low values, however, the effort (load) required for trigger pull typically is not less than 2.5 lbs. (approximately 1.134 kg.).
Some manufacturers have attempted to use leverage (i.e., by changing the geometry of the conventional trigger mechanism) to lower forces between ticker and sear, but trigger effort still remains relatively high in the prior art. Also, in the prior art, the trigger pull effort can be inconsistent (i.e., unpredictable) due to wear of the polished surfaces, poor lubrication, or lack of lubricant.
As is well known in the art, similar issues concerning the desirability of decreasing the trigger pull effort and the predictability of the trigger pull effort required for activation of the firing mechanism are raised in connection with other devices including firing mechanisms that are activated by pulling the trigger, e.g., firearms.